Certain industrial production processes and facilities require that high temperatures be maintained throughout said processes. So, the installation of proper thermal insulation is critical, particularly for those elements that comprise said facilities, such as piping, flanges, valves, filters, industrial tanks, deposits, and equipment.
Most of these elements are usually made of metal materials like carbon steel, stainless steels, or special steel alloys. These materials have a thermal expansion coefficient that causes the walls of the tanks, deposits, and equipment to expand due to high temperatures, considerably increasing in size in comparison with the size thereof at cold state. This increase in size varies, depending on the dimension of the tank or equipment, and the temperature to which they are subjected internally due to the fluid or gas that circulates inside them.
In small-sized equipment, the expansion and contraction of the walls is not very significant. The walls of this equipment expand and return to their original dimensions many times with the start-up and stop of the production process, according to the needs.
However, in large-sized equipment, the expansion and contraction of this equipment, mainly tanks, the changes are very significant and they can affect negatively to the thermal insulating systems used.
Thermal insulating methods and systems must guarantee that the thermal transmission be maintained over the life of the equipment.
Nowadays, thermal insulating systems comprise mainly four elements: support system, insulating material, covering system, and fastening and sealing means.
The support elements for the thermal insulating materials and the covering system, should be minimized as much as possible, given that the soldering of these elements to the equipment may weaken the walls of said equipment; furthermore, the thermal transmission coefficient of these metal elements with respect to the equipment is very high, leading to heat losses. Additionally, these elements must withstand the thermal expansions and contractions of the walls of the equipment without suffering breakage or sagging.
Thermal insulating materials installed must maintain their integrity after the equipment expansions and contractions, preventing the formation of gaps and joints between the materials that would create thermal bridging. Likewise, it is critical that they maintain their thickness designed during the engineering stage for the thermal calculations so that when the equipment expands and exerts pressure on the insulating material, the covering materials should not oppose resistance to the expansion, as that would considerably decrease the thickness of the insulation.
The covering system must maintain their integrity after the equipment expands and contracts, since any crack arising from the tensions of the expansions and contractions would cause joints between the sheets of the covering and would allow the insulation to be exposed to the entrance of rain water and wing that could deteriorate the qualities of the insulating materials and prevent the production process from being maintained. The mere entrance of wind between covering sheets could cause the fastenings to burst and the covering sheets to come away.
The covering sheets are fastened to each other and to the support system by means of the fastening and sealing means. These fastening means must also be designed to withstand the expansions and contractions of the walls of the tanks, deposits, and equipment due to high temperatures, without loosening and without producing tears or breakage in the covering sheets they fasten. The sealing means that seal the joints between the covering sheets must maintain their integrity after the equipment expands and contracts, to prevent rain, snow, or wind from getting in.
The insulating systems currently being adopted for the insulation of these kinds of tanks and equipment that are subjected to high-temperature are based on a reinforced design of the support and fastening systems of what would be a conventional insulating system.
Some examples of present thermal insulating systems for tanks and equipment for high-temperature are the following:                Bolt and retention washer system. These bolts are soldered to the walls of the tank or equipment, go through the insulation and perforate the covering sheets, and due to expansions and contractions, the covering tears, making ways for water and wind to enter the insulation. Moreover, on the outside of the covering the bolts are fasten by means of retention washers, these retention washers preventing the insulation thickness from expanding with the expansion of the tank or equipment.        Spacing rings system. This system comprises legs that set the distance between the wall of the tank or equipment, and the covering sheets. These legs are fastened with outer spacing rings to which the covering sheet are fastened and that must also withstand the weight of the insulating materials. The legs for the spacing rings may be soldered to the wall of the tank or equipment, or they may have another inner ring contacting the wall of the tank or equipment and to which these legs for the rings are soldered. The expansions and contractions break the fastening rings, allowing water to get inside, and additionally, this system prevents the insulation thickness from expanding with the expansion of the tank or equipment.        Mixed systems with spacing rings and bolts with retention washers.        
All systems currently being used entail that in all cases the covering sheets which cover the insulating system are fastened to the spacing rings or bolts, and are also fastened to each other on their ends (two or four ends) by means of screws and/or rivets and with sealants made of plastic materials, such as putties and silicones that must be constantly repaired when the equipment expands and contracts. With the breakage, rain water and wind can get inside and gradually deteriorate the insulating material, as well as the covering system.
There are some spacing rings systems that include an omega clip or zeta clip piece on the spacing legs, creating a spring effect, so that this clip can absorb the expansions; however, in that case, two problems arise:
First, when the omega clip absorbs the traction produced by the expansions, a decreasing of the thickness of the insulating materials occurs, diminishing the insulation quality, and putting the maintenance of the production process at risk.
Secondly, the omega clip can never absorb all of the traction, since it must have mechanical resistance to prevent it from breaking; as a result, the covering sheets continue to be subject to resisting forces that lead to breakage and joints.